1. Field of the Invention
The present invention relates to an imaging method and a device therefor. More particularly, the present invention relates to an imaging method used in, for example, an ophthalmologic examination, and a device therefor.
2. Description of the Related Art
In recent years, for a device that obtains a tomographic image of a fundus or of the vicinity of the fundus, a scanning laser ophthalmoscope (SLO) or optical coherence tomography (OCT)(optical coherence tomographic device, or optical coherence tomographic method) is used. For the OCT, methods such as a time domain OCT (TD-OCT) (time domain method) and a spectral domain OCT (SD-OCT)(spectral domain method), are available.
When the fundus is photographed by SLO or OCT, the fundus needs to be photographed through an optical structure of an eye, such as a cornea and an eye lens.
An increase in resolution causes aberration of the cornea or the eye lens to greatly influence the quality of a photographed image.
Therefore, research in adaptive optics (AO)-SLO and AO-OCT that is used to provide an optical system with a function of measuring wavefront aberration of an eye and correcting the aberration is being conducted. AO-OCT is discussed by Y. Zhang et al. in Optics Express, Vol. 14, No. 10, 15 May 2006.
In general, AO-SLO and AO-OCT are used to measure the wavefront aberration of an eye with a Shack-Hartmann wavefront sensor system.
In the Shack-Hartmann wavefront sensor system, measurement light is incident upon an eye, and a portion of the light that is reflected is received by a CCD sensor camera through a microlens array, to measure a wavefront. The shape of a deformable mirror is changed so as to correct the measured wavefront, to photograph a fundus through the mirror. It is reported that the resolution of the photographed image is increased in the photographic operation by such a device.
In measuring the wavefront aberration of the eye using adaptive optics, as described above, the measurement light is incident upon the eye, and the portion of the light that is reflected is measured.
However, since the reflectivity of the fundus is very low, and the portion of the light that is reflected by the fundus is very weak, the measurement is greatly affected by stray light from other optical elements that is incident upon the sensor.
Since the measurement light is reflected at a surface of an eyepiece disposed along the way, the reflected light is incident upon the sensor as stray light, thereby considerably reducing measurement precision.
Accordingly, in order to reduce the influence of stray light, a method of forming an optical path from the eye to the sensor with a spherical mirror is disclosed in Vol. 13, No. 21/OPTICS EXPRESS 8532/17 Oct. 2005.
However, when the optical path is formed using the spherical mirror, an optical system becomes very complicated, and the size of the optical system is increased. The spherical mirror itself is required to have high precision, and is very expensive.
Therefore, a structure in which an eyepiece portion is assembled in a lens system is discussed in Vol. 29, No. 18/OPTICS LETTER/15 Sep. 2004. In order to prevent light from being reflected at a surface of a lens, an eyepiece system is formed without passing a center axis of the lens therethrough. The eyepiece system is formed so that a light incidence position is situated away from the center of the lens when measuring wavefront aberration with a wavefront sensor and when obtaining an optical image of a test eye by OCT or SLO.